The present invention relates in general to composite plating, composite plating compositions, articles plated in such compositions, and more particularly, to a process of composite plating with polytetrafluoroethylene (PTFE) in a metal or alloy matrix where the materials used in the process contain no or essentially no PFOS (perfluorooctane sulfonate) and no PFOA (perfluorooctanoic acid).
The electroless plating of articles or substrates with a composite coating containing finely dispersed particulate matter is well documented.
Electroless plating generally involves the deposition of metal alloys by chemical or electrochemical reduction of aqueous metal ions. Through such deposition, the process of electrolessly metallizing a desired metal coating over an article or substrate is achieved.
The fundamentals of composite electroless plating are documented in a text entitled “Electroless Plating Fundamentals and Applications,” edited by G. Mallory and J. B. Hajdu, Chapter 11, published by American Electroplaters and Surface Finishers Society (1990), which is herein incorporated by reference.
As opposed to conventional electroless plating methods, in composite electroless plating, insoluble or sparingly soluble particulate matter is intentionally introduced into a bath solution for subsequent co-deposition onto a substrate or article as a coating.
Early patents related to composite electroless plating include U.S. Pat. No. 3,644,183 (Oderkerken), in which a structure of composite electroless plating with finely divided aluminum oxide was interposed between electrodeposited layers to improve corrosion resistance. U.S. Pat. Nos. 3,617,363 and 3,753,667 (Metzger et al.) utilized a great variety of particles and miscellaneous electroless plating baths. Thereafter, Christini et al., in Reissue Pat. No. 33,767, further extended the composite electroless plating technique to include the co-deposition of diamond particles. All of the foregoing references are herein incorporated by reference.
The co-deposition of particles in composite electroless plating can dramatically alter or enhance existing characteristics and even add entirely new properties. These capabilities have made composite electroless coatings advantageous for a variety of reasons including, but not limited to, increased utility in conditions requiring less wear and lower friction; facilitating the use of new substrate materials such as titanium, aluminum, lower cost steel alloys, ceramics, and plastics; allowing higher productivity of equipment with greater speeds, less wear, and less maintenance related downtime; and replacing environmentally problematic coatings such as electroplated chromium which is a significantly toxic metal.
In addition, commercially viable composite electroless coatings are essentially homogenous, uniform or regenerative, meaning that their properties are maintained even as portions of the coating are removed during use. This feature results from the uniform manner with which the particles are dispersed throughout the entire plated layer.
Commercially viable composite electroless, and conventional electroless plating processes with particles, must operate at certain levels of performance in a number of parameters. Such parameters include: plating rate of the plating bath, surface area of immersed workpieces able to be plated per volume of the plating bath, stability of the plating bath, ability to replenish the plating bath with continued used of the plating bath, lifetime of the plating bath, usually described in terms of metal turnovers, and other parameters.
Coating products using composite plating, especially metalized plating and, more particularly, electroless nickel with PTFE, has come into widespread commercialized use around the world in many industries such as high speed components, automotive applications, molds, electronic connectors, textile manufacturing components, material handling devices, machining and tooling parts, cookware and other food handling equipment, and others.
Composite plating with PTFE is accomplished by adding appropriate amounts of a dispersion containing PTFE particles into the plating bath generally containing a metal such as electroless nickel. The PTFE dispersion is formulated to break up any agglomerates, such as of PTFE, resulting from the manufacture of the PTFE and encapsulate the PTFE particles with certain chemicals that allow the PTFE to be introduced and function properly in the plating bath.
However, in recent years, health and environmental concerns have been raised about the inclusion of certain materials in PTFE dispersions, including PFOS and PFOA, that are used in composite plating systems. In particular, some materials in PTFE dispersions become included in the plating, and these materials later migrate from the plated objects into or onto other items, including humans and animals. For example, PTFE is used in plating cookware and, at times, small quantities of the plating material, including PTFE and any materials in the PTFE plating, may be absorbed by the foods prepared in the cookware. Another example is in components used in consumer and industrial products such as automotives, electronics, and others which may ultimately be disposed and the disposition may lead to exposure or transfer of the PFOA or PFOS into the environment.
According to the United States Environmental Protection Agency, “Perfluorooctanoic acid (PFOA), also known as “C8,” is a synthetic chemical that does not occur naturally in the environment. It has special properties that have many important manufacturing and industrial applications. The EPA has been investigating PFOA because PFOA is very persistent in the environment, is found at very low levels both in the environment and in the blood of the general U.S. population, remains in people for a very long time, and causes developmental and other adverse effects in laboratory animals. Major pathways that enable PFOA, in very small quantities, to get into human blood are not yet fully understood. PFOA is used to make fluoropolymers and can also be released by the transformation of some fluorinated telomers. However, consumer products made with fluoropolymers and fluorinated telomers, including Teflon® and other products, are not PFOA. Rather, some of them may contain trace amounts of PFOA and other related perfluorinated chemicals as impurities. The information that the EPA has available does not indicate that the routine use of consumer products poses a concern. At present, there are no steps that EPA recommends that consumers take to reduce exposures to PFOA. In 2006, EPA and the eight major companies in the industry launched the 2010/15 PFOA Stewardship Program, in which companies committed to reduce global facility emissions and product content of PFOA and related chemicals by 95 percent by 2010, and to work toward eliminating emissions and product content by 2015.”
In addition, the United States Environmental Protection Agency states that, “In January 2005, the EPA Office of Pollution Prevention and Toxics submitted a Draft Risk Assessment of the Potential Human Health Effects Associated With Exposure to Perfluorooctanoic Acid and Its Salts (PFOA) to the EPA Science Advisory Board (SAB) for formal peer review. EPA sought this early stage scientific peer review from an outside panel of experts in order to ensure the most rigorous science is used in the Agency's ongoing evaluation of PFOA. That draft was preliminary and did not provide conclusions regarding potential levels of concern. The SAB reviewed the information that was available at the time, and suggested that the PFOA cancer data are consistent with the EPA Guidelines for Carcinogen Risk Assessment descriptor “likely to be carcinogenic to humans.”
Regarding Perfluorooctane sulfonate (PFOS), The Organization for Economic Cooperation and Development has stated that “Sufficient information exists to address hazard classification for all SIDS [Screening Information Data Set] human health endpoints. PFOS is persistent, bioaccumulative and toxic to mammalian species. There are species differences in the elimination half-life of PFOS; the half-life is 100 days in rats, 200 days in monkeys, and years in humans. The toxicity profile of PFOS is similar among rats and monkeys. Repeated exposure results in hepatotoxicity and mortality; the dose-response curve is very steep for mortality. This occurs in animals of all ages, although the neonate may be more sensitive. In addition, a 2-year bioassay in rats has shown that exposure to PFOS results in hepatocellular adenomas and thyroid follicular cell adenomas; the hepatocellular adenomas do not appear to be related to peroxisome proliferation. Further work to elucidate the species differences in toxicokinetics and in the mode of action of PFOS will increase our ability to predict risk to humans. Epidemiologic studies have shown an association of PFOS exposure and the incidence of bladder cancer; further work is needed to understand this association. Sufficient information exists to address hazard classification for all SIDS environmental endpoints. PFOS is persistent in the environment and has been shown to bioconcentrate in fish. It has been detected in a number of species of wildlife, including marine mammals. Its persistence, presence in the environment and bioaccumulation potential indicate cause for concern. It appears to be of low to moderate toxicity to aquatic organisms but there is evidence of high acute toxicity to honey bees. No information is available on effects on soil- and sediment-dwelling organisms and the equilibrium partitioning method may not be suitable for predicting PNECs [Predicted No Effect Concentrations] for these compartments. PFOS has been detected in sediment downstream of a production site and in effluents and sludge from sewage treatment plants.”
The United States Environmental Protection Agency is also actively investigating the levels of contamination of PFOS in the environment from the land to water supplies, animals, animal products such as milk, and its effect on animal and human health.
Specifically, it is desirable to reduce or eliminate PFOA and PFOS from such systems.
Accordingly, there is still an unsolved need for further improvements in composite PTFE plating solutions and methods, whereby PFOS and PFOA are eliminated or greatly reduced.